Draw the panel as a panel

Five things a wall panel showed that a wall panel should not.

**A tile's body no longer clips.** It scrolled, and a box that scrolls
also cuts whatever crosses its edge — which took the glow off a lit
button at exactly the width where the button filled its tile, and off a
gauge's arc at exactly the height where the dial filled its own. Only
what is written or listed asks for a scroller now; everything else is a
picture drawn to fit, and what overflows is left to the frame, which
clips at the tile's edge where a shadow has already faded out. The
slider's phantom scrollbar goes with it.

**The selector is a selector.** Named for what it does rather than what
it is, and the choice it is holding is held in the dashboard's own
primary — a pill that slides between the options rather than a grey one
that had to be looked for. The stored type is untouched, so no document
changes meaning.

**The arrangement is held off the panel's edges**, by the same distance
it holds between two widgets. The ground is not held off with it: a
background covers the whole panel, and only what is arranged on it has
a margin. No stored panel loses a row to it.

**The rail is drawn on the panel.** It was chrome bolted to the edge of
the screen beside the canvas — in the app's own design rather than the
dashboard's, and on a scaled canvas not even lined up with it. It now
takes a column out of the canvas the way the margin does, scaled with
it and wearing its look. Which cell each widget sits in is unchanged;
only how big a cell is.

Two of these were the same mistake twice: an unlayered rule stating
`position` for everything wearing a class — `.gl-surface` on a rail
placed by a utility, and a blanket lift over every child of a pressable
on a pill placed by `layoutId`. Both now say it one element at a time.

frontend/src/components/Dashboard/ui/material/Surfaces.tsx

@@ -58,6 +58,7 @@ export function Frame({
   title,
   issue,
   grip,
+  scroll,
   selected,
   onClick,
   children,
@@ -85,7 +86,9 @@ export function Frame({
           {issue ? <Issue issue={issue} /> : null}
         </div>
       ) : null}
-      <div className="dui-frame-body">{children}</div>
+      <div className={cn("dui-frame-body", scroll && "dui-frame-scroll")}>
+        {children}
+      </div>
       {/* No header to sit in, so the fault takes the corner instead — a widget
           drawn without its title still says when it is mis-wired. */}
       {!title && issue ? (
@@ -121,7 +124,7 @@ export function Rail({ entries }: RailProps) {
       aria-label="Dashboards on this panel"
       data-testid={TESTID.rail}
       className={cn(
-        "m3-rail pointer-events-auto absolute inset-y-4 left-4 z-10 flex w-14 flex-col items-center gap-1 p-2",
+        "m3-rail pointer-events-auto absolute inset-y-3 left-3 z-10 flex w-12 flex-col items-center gap-1 p-1",
         // More dashboards than the column is tall still scroll, but no bar is
         // ever drawn: a wall panel is swiped, and there is no room for one.
         "overflow-y-auto [scrollbar-width:none] [&::-webkit-scrollbar]:hidden",